few other things:
1) clear the browser history and cache - that can make a huge difference for net related stuff
2) change XP performance settings to get rid of the cute animation that has no purpose at all:
* right click on My Computer
* Select Properties
* Click on ADVANCED tab
* Click on SETTINGS in the Perofrmance section (first settings button)
* Click on "Adjust for best perofrmance" and click OK
3) As others already mentioned, DEFINITELY run something to detect spyware. That can make a huge difference